This application relates to a process for vapor phase hydrogenation at reaction temperature in the range between 200.degree. and 400.degree. C. of a nitroaromatic compound, of the group consisting of nitrobenzene, nitrotoluene, and mono- and poly(chloro-, bromo, fluoro-)nitrobenzenes and nitrotoluenes, to the corresponding aminoaromatic compound comprising conducting said nitroaromatic compound with a catalyst consisting essentially of titanium dioxide.
It is known (Etzel, J. Physical Chem. Vol. 32, pages 852-860) that titanium dioxide is a good catalyst for reduction of nitrobenzene by hydrogen gas, especially at a temperature of about 300.degree. C.
U.S. Pat. No. 3,253,038 of May 24, 1966 to Wise discloses use of hydrogen sulfide for reduction of nitrobenzene in either liquid phase at about 200.degree. C. or vapor phase at about 300.degree. C. and atmospheric pressure over a zeolite catalyst in the sodium form. In the examples, the conversion of nitrobenzene to aniline is quite low.
U.S. Pat. No. 3,255,252 of June 7, 1966 to Gold relates to liquid phase reduction of nitroaromatic compounds by hydrogen sulfide using, in a homogeneous catalysis process an amine catalyst; and in a heterogeneous catalysis, a combination of silica and amphoteric metal oxide such as alumina, thoria or zirconia. Again in this patent, a large part of the nitrobenzene charge is recovered unreacted, per the Examples.
U.S. Pat. No. 4,059,627 of Nov. 22, 1977 to Kritzler et al. discloses in column 1 that hydrogenation of chloroaromatic compounds is accompanied by more or less extensive dechlorination with accompanying loss of yield and high corrosiveness due to the hydrogen chloride formed. The patent cites prior art use of noble metal sulfides or sulfited noble metal catalysts. In the invention, a noble metal on a carbon support is used in presence of a small proportion of a thioether functioning as an inhibitor of the dechlorination (column 4, line 63--column 5, line 2). The temperatures disclosed are 30.degree.-200.degree. C. (column 5, line 45) and hydrogen pressure is 5-150 atmospheres (column 5, line 15).
U.S. Pat. No. 4,128,586 of Dec. 5, 1978 to Ratcliffe discloses catalytic reduction of aromatic sulfonyl halides with hydrogen sulfide, to form aromatic thiols.